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Multi-dimensional array and pointers in C++?

Hi,
In 1D I can declare an array like,

int *image = new int[W*H];

But in 2D how can I declare an array?

int *image = new int[W][H]; -- is it wrong??

Answer 1

int *image = new int[W][H]; -- is it wrong??

It will NOT compile. You should compile your code first, to know the answer of your question.

I think you want to do this:

//memory allocation
int **image = new int*[W];
for(size_t i = 0 ; i < W ; i++ )
   image[i] = new int[H];

//use it as
 for(size_t i = 0 ; i < W ; i++ )
    for(size_t j = 0 ; j < H ; j++ )
          image[i][j] = some_value;
int value = image[20][30]; //get value at (20,30) assuming 20 < W and 30 < H

//memory deallocation
for(size_t i = 0 ; i < W ; i++ )
   delete [] image[i];
delete [] image;

But then why do all these when you’ve std::vector? You could use it which will do all these nasty thing itself. Here is how you should be using std::vector:

std::vector<std::vector<int> > image(W, std::vector<int>(H));
for(size_t i = 0 ; i < W ; i++ )
    for(size_t j = 0 ; j < H ; j++ )
          image[i][j] = some_value;
int value = image[20][30]; //get value at (20,30) assuming 20 < W and 30 < H